1. Field of the Invention
The present invention relates to a fuel injection apparatus and applied to a diesel engine, etc. equipped with an accumulator fuel injection apparatus, the apparatus being composed such that; high pressure fuel pumps are provided each of which compresses fuel introduced into its plunger room to high pressure by its plunger fitted in its plunger barrel and reciprocated by means of a fuel cam and discharges the compressed fuel at timing controlled by an electromagnetic valve to supply the compressed fuel to a common rail, and high pressure fuel accumulated in the common rail is injected periodically at determined injection timing into each of the cylinders of the engine, and a method of operating the engine equipped with the apparatus.
2. Description of the Related Art
An accumulator fuel injection equipment used in a diesel engine is provided with high pressure fuel injection pumps each of which compresses fuel introduced into its plunger room to high pressure by its plunger fitted in its plunger barrel and reciprocated by means of a fuel cam, and high pressure fuel accumulated in a common rail is supplied to each of fuel injection valves to be injected periodically at determined injection timing into each engine cylinder.
In an accumulator fuel injection apparatus like this, discharge duration of high pressure fuel from each of the high pressure pumps is controlled by controlling opening/closing of a low pressure side fuel feed passage by means of an electromagnetic valve provided to each pump as disclosed for example in Japanese Laid-Open Patent Application No. 64-73166 (patent literature 1) and Japanese Laid-Open Patent Application No. 62-258160 (patent literature 2).
In FIG. 3B represents a diagram showing a fuel cam lift and opening/closing of the electromagnetic valve vs. crankshaft rotation angles in the electronically-controlled accumulator fuel injection apparatus disclosed in the patent literature 1.
In FIG. 3B, the fuel cam lifts and opening/closing timing of two high pressure fuel pumps among a plurality of the high pressure fuel pumps are shown. As shown in the drawing, the conventional electronic control accumulator fuel injection apparatus is composed such that the plurality of high pressure fuel injection pumps (No. 1 pump and No. 2 pump in this example of FIG. 3B) operate in the same operation condition all over engine operating range, the electromagnetic valve is closed on the way the cam lift is increasing to begin fuel discharge from the high pressure fuel pump, and opened when the cam lift is near its maximum to allow high pressure fuel in the plunger room of the high pressure pump to spill out to the fuel feed line (low pressure side fuel line).
In prior arts disclosed in the patent literature 1, and 2, etc., as shown in FIG. 3B, all of a plurality of high pressure fuel pumps (No. 1 and No. 2 pumps in this example) are operated to discharge fuel by closing their electromagnetic valves and to allow remaining high pressure fuel in the plunger room to spill to the fuel feed line at injection end by opening their electromagnetic valves in all over the engine operation range.
The number of discharging and spilling is determined by the product of the rotation number of the fuel cam, the number of cam lobes per fuel cam, and the number of the plungers.
As the high pressure fuel remaining in the plunger when fuel injection ends is spilled to the fuel feed line, the energy consumed to compress the spilled fuel is wasted to the fuel feed side.
As mentioned above, in the prior arts, all of the high pressure fuel pumps discharge high pressure fuel to the common rail and the high pressure fuel remaining in each of the plunger room at the end of fuel injection from each injection nozzle is spilled by opening each electromagnetic valve, so that the energy consumed to compress the spilled fuel is wasted to fuel feed side, resulting in decreased energy efficiency.